U.S. Pat. 4,337,197, issued June 29, 1982 describes O-sulfated .beta.-lactam hydroxamic acids having antibacterial activity. Preferred compounds, as disclosed by the patent, have the formula ##STR5## wherein R'.sub.1 is acyl, R'.sub.3 and R'.sub.4 are the same or different and each is hydrogen or alkyl, and M.sup..sym. is hydrogen or a cation. Several processes for preparing the above compounds are described including a process which utilizes an intermediate having the formula ##STR6## wherein A' is a nitrogen protecting group and Y' is benzyl or pivaloyl. As described in the patent, the hydroxyl group of the above intermediate is converted to a leaving group, using, for example, a classical reagent such as methanesulfonyl chloride. The fully protected compound has the formula ##STR7## (L' is a leaving group), and can be cyclized by treatment with base, e.g., potassium carbonate, to yield a compound having the formula ##STR8##
Alternatively, the patent describes the single step cyclization process which comprises treatment of an intermediate having the formula ##STR9## with triphenylphosphine and diethylazodicarboxylate.